Just droped off about 1000 bdft of Walnut and RO at the mill. Was talking (BSing) with the sawyer about weighting the lumber for drying. The sawyer said he used nylon ratchet straps instead of weights, he air dries his wood in old tobacco barns.
This got me to thinking about using either the same straps or even the metal banding straps to bind the stack befor it goes in to the kiln. The mosture content would/could be a problem reacting the the metal banding. I don't see any problems with the nylon straps outside of the extra cost to buy them and the time to bind the load.
Anybody got some experience using strapping to bind a kiln load?
The ratchet straps can be adjusted to compensate for the pile shrinking as it drys. A banding strap will be of no value after a couple of days. My own personal experience is that weighing down a pile has no real effect in the kiln. If a board has a mind to twist it does. I have gone to drying with no weight at all in the kiln and have not noticed any problems.
I have to agree with Horselogger.
If its gonna move its gonna move.
Steal banding will also cause staining on the RO.
Mike.
The amount of warping is directly related to how slow the wood is dried. The faster it is dried the less warping. Often kiln opertors stuff as much wood in the kiln as they can. With the way air flows down the plenum chamber, the top foot or two gets very little airflow . Therefore. very little dryng occurs there. This is why the top layers warp. The old story of, penny wise pound foolish. There is very little elastic movement in metal strapping and therefore would be of no value.
JimF Welcome to the forum. Would you fill in your Bio for us, please?
I am curious about your comment ""The faster it (wood) is dried the less warping.""
Would you clue us in to a resource that supports that observation? Thanks.
Warpage is caused by uneven or unrestrained shrinkage. By drying fast the large protion of the centerof the board restrains the shrinkage of the shell. With the shell dry, stiff and strong, it restrains the next layer from warping and so on until the center is dry. By drying slow, the majority of the board shrinks at the same time having nothing to restrain it from warping. Even reaction wood can be dried into a straight board if dried quickly enough. Bear in mind species like oak which is surface check prone and cotton wood that is collapse prone need to dried with more concern for speed.
I dunno, maybe its just the way I am reading that last post, but it sounds like a good description of "how to case harden lumber" ???
I'd say that Jim has a point. In conventional and DH kilns, you are going to have the shell dryer than the core. That's the nature of the beast. If you dry fast enough, this could be advantageous as he says. But, as Horselogger says, the conditions which create 'fast' drying could easily overdry the shell and then you end up with case hardening.
I wonder who else will start posting at this forum? about time for Gene? :D
Unless you are using vacume drying you can not avoid casehardening. It occurs whether you dry slow or fast - air-drying, dh, solar or conventional. Wood only dries from the outside-in.. When you dry slowly,air-drying, solar-drying and poorly controlled kiln drying, you risk more damage and warpage than if you dry fast with good control. Naturally, drying fast with poor control you are demanding a disaster.
Interesting JimF. What you are saying seems to go against conventional wisdom but makes sense.
Welcome to the forum and please continue to give us your insight!
Actually it is not against conventional wisdom. With the advent of the energy crisis the solar kiln came into fashion. And to sell that idea the conventional wisdom was pushed out the door. Now we hear the altered wisdom.
To support the idea of drying fast, I have a patent for monitoring/control of wood drying that reduces the drying time by more than 35%. While do so the drying stresses are actually reduced in the end. And you end up with brighter and more defect free lumber.
JimF
Do you have a resource (publication of results) that supports the "altered wisdom" ?
:P
You are presenting some interesting (teasing?) ideas, that could use some additional support. Is the patent idea available on the market? Did you do vacuum drying testing?
Thanks for filling out the bio.
Maybe too many questions!
8)
JimF.
Please tell us more.
Can your patented idea be used in vacuum drying?
Hey Jim,
You have an audience. And at this forum, no know-it-all is going to shoot you down. I may play the devil's advocate at times but there is no guru here.
Den
Den.
Who you calling the "no know it all"?
I'm not referring to any hot-head. ;) nope! :D
Better not be!Most everything Ive learned about vac drying Ive learned from you!
And I would call you a guru.An Old guru!! :D
Thanks for the interests in my ideas.
Beenthere,
no it is not on the market yet. It is easy to have a great idea. It is another thing to get financial backing. Venture capitlaists only come on the scene when the inventor is filing for bankrupcy, after all the hard work of development is done. And regional economic development committees are only interested in flashy high tech stuff like biotechs because it looks good on their records, not improvement of communities .
I'm told to find a doctor or airline pilot. They have lots of money and will go for anything a good salesman puts in front of them. Anyone know of any doctors or airline pilots looking to invest?
Den,
I like devil's advocates. They help bring out the fine details of a discussion.
If you are controlling properly and are drying fast you can not over dry the shell. That is controled by the EMC in the kiln and is what equalization is partially for.
The "altered wisdom" is air-drying is gentle to the wood - Myth 1. Solar-drying is different from conventional drying - Myth 2. To name some.
If you air dry white pine or maple, for example, the center of the stack is likely to get blue stain or sticker stain. If you air-dry oak, you are sure to get large surface checks because of the up and down trends of the EMC. The up and down trends of the EMC only makes the surface checks worse, that have developed from the lumber being exposed to the sun or breeze on the green chain.
Solar drying is claimed to be diferent than conventional and is gentle because of the EMC rises at night. However, in conventional kilns the airflow is switched about avery 6 hours; causing the entering air side to become the exiting air side. The causes the EMC to go up and down at the sides of the stacks. The cyclic gain and loss of moisture in the wood at these points can be measured and the shrinkage and swelling can be measure as a result. Because in a conventional kiln this can be controlled to some extent but is not in a solar kiln, the wood is exposed to more sever conditions in the solar kiln. The surface checks will be extended further into the board than in a conventional kiln. The some of the same people that promote solar-drying say never to start the kiln drying by adding steam to bring the EMC to set point because of the surface check problem.
I have never had the oportunity to try the new method out on vacuum drying. As has been mentioned here there are numerous methods to vacuum dry. They all produce important differences in terms of control and stress development. In a past post I generalized vacuum drying as not producing casehardening. It depends on the method. If you use conductive heat source, like heat blankets or hot water pipes, you still produce cashardening. After the initial pull of a vacuum, the water still only evaporates from a liquid boundary line. The heat can only travel through the surface of the wood to the water; heating up the water nearest to the surface first.
Radio frequency while enters the dry portion of the wood and heats up the water inside it mostly only heats up the water nearest the surafce of the wood. Therefore it produces casehardening. However, there is one company that claims the frequency that there equipment uses penetrates the wet wood more evenly and heats up the water more evenly. I have not seen the data for that to know enough about it to comment on it.
The intermitantly heated method that has been mention here alot is another species all together and is much more complitcated. I have not sat down to study how things occur within it yet.
Speaking on vacuum drying. There is one method that intrigues me for very small operators. It encloses the wood in a plastic bag, in essences and immerses it in hot water. Then a vacuum is pull on the bag. This is a inexpensive way to provide continuous heating. Admittedly in practice it is for small chunks or a small number of boards, but it is a method most people can fabricate and operate. It is patented and a company is working on getting it on the market.
jimF.
What if one was to pre-heat in a vac kiln before he pulls a vacuume?Would this not bring the whole piece of wood up to the same temp?
yes, and the whole piece should loss water some what evenly. But not all the water. So the concern is after the initial vacuum pull, how is it heated? With intermittant heating system mentioned here, it seems like this would happen each time, but with repeated occurances things can become complicated quickly. Which is why I hold back my opinion in this instance.
To stir the pot some, what are the concerns during drying - in all systems of drying?
jimF.
With square drying in a vac kiln the concern was honey comb and surface cracks.In flooring blanks and lumber the concern is with stress and un even moisture content.
Also in vac drying some people complain about the sap wood being to bright and the MC being to low.
There was a problem with bow in vac dried squares but that is an easy problem to fix.
I may also add that in the last 2 weeks I found that stress is not that big of a deal in vac dried lumber.